Aortocaval fistula

Aortocaval fistula is a rare and devastating complication of abdominal aortic aneurysm (AAA), where in the aneurysm erodes into the inferior vena cava.

Epidemiology

Spontaneous rupture of an abdominal aortic aneurysm into the adjacent inferior vena cava occurs in <1% of all aneurysms and in ~3% of ruptured aortic aneurysms ¹.

Clinical presentation

The features can be very atypical leading to a delay in diagnosis. The various factors that influence the clinical presentations are the origin, size, location and duration of the fistula:

• backache
• high output cardiac failure 
• bilateral pedal edema (venous hypertension in the lower half of body)
• hepatic failure
• renal insufficiency (reduced renal blood flow)
• hematuria
• continuous bruit in the abdomen ⁴

Radiographic features

Aortography is the modality of choice. Color Doppler, CT and MRI may also demonstrate the same non-invasively. At times, the presence of a mural thrombus may obstruct the fistula.

Treatment and prognosis

Urgent surgical exploration and repair. Operative mortality of spontaneous aortocaval fistula is about 20 to 55%, figures being high predominantly due to delayed diagnosis or misdiagnosis.

Differential diagnosis

• aorto-left renal vein fistula